EXTRATERRESTRIAL LIFE

Earth is the only world we know of that supports life. But
is there extraterrestrial life – life beyond Earth – elsewhere in
Universe? It is possible that there is, or has been, other life in our Solar
System, perhaps on Mars or Europa. But to find intelligent life, astronomers
are looking much further away. In research programmes called SETI (Search for
Extraterrestrial Intelligence), they monitor the skies for signals from
intelligent life in deep space.

THE VOYAGER MESSAGE

The two Voyager spacecraft travelling through the Solar System will
soon leave it behind and enter interstellar space – space between the stars.
Each spacecraft carries a disc on which images, natural sounds, speech, and
music have been recorded. It is hoped that, one day, intelligent beings from
another world may find a disc and get a picture of life on Earth.

LIFE ON EUROPA?

Jupiter’s large moon Europa has a flat surface of pink ice. It is criss-crossed with cracks, which
may have been caused by the movement of a liquid ocean beneath the surface,
melted by energy caused by the powerful tidal effects of Jupiter’s
gravity. This has led to speculation that life may exist on Europa.

SCANNING THE SKY

The radio telescope at Arecibo in Puerto Rico is one of several that
has been used to listen for signals that might be from other civilizations in
space. As part of a SETI programme called Project Phoenix, millions of radio
channels have been scanned simultaneously. Radio waves are studied because they
are able to travel a long distance without interference.

PRIMITIVE LIFE

The earliest forms of life on Earth appeared nearly four billion
years ago in the form of cyanobacteria (blue-green algae). These organisms are
still found today in Western Australia, where they form distinctive mounds
called stromatolites. The evolution of life began from these single-celled
organisms. On other worlds life may exist in a similar, primitive form.

LOOKING FOR SIGNALS

Looking for a signal in space that may have been sent by intelligent
extraterrestrials is like looking for a needle in a haystack. Huge quantities
of data are received, which must then be processed. Through the SETI@Home
project, ordinary computer users can help with this task.

EXTRASOLAR PLANETS

A planet similar to Jupiter has been found circling star HD 187123.
It is known as an extrasolar planet – a planet beyond our Solar System. A SETI
project directs its radio telescopes at stars known to have planets, and stars
like our Sun, as these are the most likely to have planets capable of
supporting life.

THE DRAKE EQUATION

American radio astronomer Frank Drake, a SETI pioneer, drew up a
list of key factors necessary for intelligent life to evolve on a planet. The
list, named the Drake Equation, is a basis for calculating the number of
possible civilizations in our galaxy. However, the factors are based on only
one example of life on a planet, our own. We do not know if these factors will
apply to life forms on other planets. Optimists estimate that there are
millions of civilizations in the Milky Way. Pessimists estimate that there is
just one – our own.

How many stars in the galaxy are stable over the billions of years necessary for life to evolve?

How many of these stars give birth to stable planetary systems around them?

How many of these planets have suitable conditions for life?

On how many of these planets does life begin and take hold?

On how many of the planets does intelligent life evolve and become able to communicate?

On how many of the planets with intelligent life are conditions right to create a technology suitable for communication across the Universe?

How many potentially advanced civilizations are wiped out by natural or self-inflicted disasters?